That's because the DC Universe won't be the real world. The technology should be more advanced to fit the world. It's the same thing with Iron Man over at Marvel Studios. The world is still relatively low-tech like you said, and yet Stark is able to create all sorts of gadgetry. Same with S.H.I.E.L.D., who tapped into a cosmic energy source and generated a portal with their technology.

Well, as long as the advanced technology fits within our world, for instance, we see it created, or we know that it came from space, that works just fine. But if some human inventor takes human science and makes something ridiculously superhuman in a limited amount of time, it's going to be a turn off for me, it's going to be cartoony. Stark is making armor and power sources, things we have, he just makes them better. Lex can do stuff like that and not be cartoony to me, but if he starts making homemade phantom zone projectors and teleportation devices and mind control machines, it's going to be whack. If, like the portal with the Tesseract (SHIELD didn't generate that by the way, it was cool that they couldn't understand it fully), Lex takes something alien (ie Superman's DNA, Zod's tech) or whatever and improves on it (Bizzaro, Metallo, etc), that's cool. That makes sense.